1. Technical Field
The present invention relates to a projection optical system, which is capable of converting the aspect ratio of a projection image, and a projector having the same.
2. Related Art
There are front-type converters that are converters for aspect ratio conversion used in projection optical systems of projectors and are disposed to be able to advance and retract relative to the original positions on the front face, that is, the image-side front of the projection optical systems.
However, some of the projectors may perform, for example, tilt projection to project an image in a state where the center of the image element is out of the optical axis of the projection optical system. In such image projection, the deviation between the optical axis and the center of the image element may cause change in the center position of the screen image on the screen which is the projection target surface in accordance with conversion of the aspect ratio. That is, by converting the aspect ratio, the positional relationship between the center of the screen and the optical axis is changed. As a result, the change may cause a situation in which the entire projection image is also projected at a position deviated from the center of the screen.
In addition, there are rear-type relay systems that are converters for aspect ratio conversion that are not used in the projection optical systems of the projectors but in image capturing optical systems such as cameras and are detachably disposed on the image sides of the imaging optical systems (refer to JP-A-2005-221597).
However, in the image capturing optical system disclosed in JP-A-2005-221597 or the like, it is not normally assumed to adopt an aspect in which the center of the image element is deviated from the optical axis of the projection optical system in a similar manner to the tilt projection. Accordingly, although a configuration in which the relay system is disposed on the rear side in a similar manner to JP-A-2005-221597 is used in the projection optical system of the projector, there is a problem of the positional deviation of the projection image caused by the conversion of the aspect ratio similarly thereto.